In the journal "SEV-Bulletin" No. 63, part 21, 1972, there is a review of maintained energy supply systems for such loads. These systems have either a standby generator set or a continuous current supply installation provided between the normal main energy supply system and the loads. In a system with a standby generator set the energy is usually provided by the main supply while the standby set is "off" but, if the main supply fails or is disturbed (e.g. resulting in a voltage reduction), the standby set automatically comes into operation to maintain the proper supply. The standby or auxiliary energy source consists for example, of one or more diesel engines with generator(s) or of one or more inverters and batteries. A system such as this has a relatively high efficiency but there is invariably a substantial time lag between the detection of failure or disturbance of the main supply and the resultant bringing into operation of the auxiliary supply and this is often undesirable particularly in the case of loads which are sensitive to even very brief voltage fluctuations (some loads of the kind referred to are affected by voltage fluctuations having a duration even shorter than a quarter cycle of the of the alternating waveform of the energy supply). Furthermore, in the known systems of the kind described above, the auxiliary supply only comes into operation when the main supply fails or its voltage fails to an unacceptable level while distortion of the supply waveform and voltage increases for example are ignored.
The other kind of maintained energy supply system, i.e. those comprising so-called continuous current supply installation, were produced in order to overcome the above-mentioned disadvantage of the auxiliary generator system. In them, an energy store is provided between the load and the normal energy supply system. This store receives energy from the main supply system and gives it up to the loads during normal operation. i.e. so that in effect, the store can be regarded as the energy supply for the load at all times but normally the store is itself being replenished by the main supply. If the main supply fails, the store can nevertheless maintain the supply of energy to the load (until of course the main supply has been out of action for so long at any one time that the store becomes empty). Due to this "interposition" of energy sources, the loads are completely independent of any disturbances, e.g. voltage reductions or voltage rises, and distortion, emanating from the main energy supply system. However, the great disadvantage of such systems is their low efficiency, so that the cost of supplying energy to complicated loads is enormously increased.
The invention has for its object to retain the advantages of a continuous energy supply system and yet to achieve the maximum possible efficiency.